Method for measuring the weight of bulk goods loaded by a hydraulic excavator

ABSTRACT

The present invention is directed towards a method for measuring the weight of bulk goods loaded or, alternatively, loading performance over time of hydraulic earth moving machines, excavators or similar machines which are provided with a hydraulically operated material loading scoop. Typically, these loading scoops rotate about and are supported on a loading arm. The scoop is controlled and tilted by a hydraulic piston-cylinder unit. The determination of the weight of bulk goods loaded or of the loading performance of the excavator is often required by the operator and the manufacturer of the apparatus, both for the determination of the performance of the apparatus per work shift, or for the computation of the fully loaded weight of a transport vehicle used in carrying away the bulk goods. The measured values used in determining the weight of the loaded material are the pressure in the piston-cylinder unit, arragned between the loading scoop and the loading arm, and an angle defined by the line passing between the pivot point ofthe shovel and the center of gravity of the empty shovel with respect to a horizontal line. These values are fed into a computer, and by using certain predetermined values and a simple force equation, the weight of the contents of the scoop is calculated and then visually indicated. The weight may be accumulated, and then indicated on command, in order to determine the total loaded quantity of bulk goods. Alternatively, the accumulated weight can indicate the loaded performance of the apparatus if displayed at predetermined time intervals.

RELATED APPLICATIONS

This is a continuation-in-part application of U.S. patent applicationSer. No. 389,716, filed June 18, 1982.

BACKGROUND OF THE INVENTION

The present invention is directed toward a method for measuring anddetermining the loading performance over time to total loaded quantityof bulk goods moved by hydraulic excavators or similar loading or earthmoving devices having hydraulically operated arms. These earth movingvehicles typically have an extending loading arm and a loading scooprotatably arranged about it. A hydraulic piston-cylinder unit isprovided between the loading scope and the loading arm for rotativelymoving the scoop into its loading and unloading position. According tothe present invention, the apparatus is provided with a mechanism formeasuring the pressure of the hydraulic cylinder and means for measuringan angle defined by a line connecting the pivot point of the shovel andthe center of gravity of the empty shovel in relation to the horizontal,these values being then used to caculate the weight of the load in thescoop.

Operators and manufacturers of the earth moving or bulk goods carryingequipment find the direct measuring of the loading performance,particularly of large earth moving machines, to be of great interest andit is, therefore, in great demand. It may well be of importance to know,for example, the fully loaded quantity of a transport vehicle loaded bya hydraulic excavator, specifically in order to arrive at the weight ofthe load. It may also be of interest to know the performance of theexcavator or of the operating crew per shift and per unit time interval.

DESCRIPTION OF THE PRIOR ART

There are known apparatus which can determine the loading moment of ahydraulic excavator, specifically for the purpose of avoidingoverloading of the machine. The loading moment depends on the contentsof the scoop shovel and on the working angle of the shovel. The load iscustomarily determined by measuring the hydraulic pressure in theloading arm and the angular position of the arm by potentiometers. Whenthe upper limit boundary value is exceeded, a signal is either given orthe apparatus is automatically switched off.

An apparatus for determining the weight of the contents of a shovel isknown from German disclosure document No. 30 20 323. The proposal madethere is based on the measurement of pressure in the arm cylinder whichis taken at a certain position of the angle of the loadng arm.Measurements based on this principle, however, lead to substantialmistakes. By measuring the pressure in the arm cylinder, the entireweight of the apparatus is taken into consideration which results insubstantial measuring distortions. The disortions are greater still whenthe apparatus is moving during the measuring process. In that case, apressure is measured in the arm cylinder which is substantially greaterthan the pressure required to hold the apparatus in position. Inaddition, in a measuring method according to the cited reference,accurate and reliable measuring is only possible on level ground becauseoverload indications are otherwise unavoidable because of the movementof the center of gravity when the machine is located on sloped surfaces.Loading performance over time or accumulated loading measurements arenot provided for in the conventional apparatus.

The present invention is directed to a method for accurate measuring ofloading quantities picked up by the loading scoop of a bulk goods orearth excavator type mechanism. Alternatively, the total amount ofloaded bulk goods over a predetermined time interval is a desiredparameter to be determined according to the present invention.

SUMMARY OF THE INVENTION

It is possible to solve the problems of the existing prior art measuringmethods and to accomplish the desired purpose of the present inventionin a particularly advantageous manner through the proposal of theinvention. In this manner, the weight of the bulk goods loaded by thescoop and the loading performance, i.e., the total weight of the goodsloaded over time may be very accurately determined. Since, according tothe invention, the measuring is done directly adjacent to the scoop, thepossibility of substantial errors is nearly eliminated. Even moreaccurate and reliable meaasured values can be obtained if the hydraulicpressure in the piston-cylinder unit is not only measured on one side ofthe cylinder but, in addition, if it is also measured on the side of thepiston rod, so that differences in pressure in the cylinder will notdistort the perceived loaded weight of the excavator shovel.

It may be of interest in loading a vehicle used to transport theexcavated bulk materials to know the total weight of the loaded quantityactually placed into this vehicle. This can be realized by anothercharacteristic of the present invention, wherein it is proposed toaccumulate the previously determined individual weights of the contentsof the loading scoop.

The full weight of the load contained in the vehicle used to transportthe loaded bulk goods can easily be determined by counting the number ofloaded scoops, after accumulation of the loaded weights. The totalaccumulated load weight can then be displayed, on demand. Acharacteristic work motion of the apparatus, such as, for example, theopening of the scoop lid can be used for counting the number of scoopsloaded into the transport vehicle.

One proposal, according to a specific characteristic of the presentinvention, is that in order to determine the loading performance, thedetermined weights of the contents of the scoop of several processingsequences are accumulated and indicated in relation to a predeterminedtime interval.

In this manner, the performance of the excavator may be directly readfrom a built-in timer so that, for example, the performance for loadingone single vehicle, but also during an extended time period, for examplea work shift, may easily be determined. All that is required for thatpurpose is merely to feed in the beginning and the end of the timeinterval.

Another advantageous characteristic of the present invention lies in theproposal that, while the pressure in the piston-cylinder unit and theangle are being measured, the motion of the loading scoop is brieflyinterrupted by a control device for the duration of the measuringprocess. This eliminates excesses in pressure due to motion of the scoopwhich would otherwise distort the measured value. To this end, it isenough to stop the motion of the scoop for the duration of, for example,only 0.75 seconds.

An exact measuring value is obtained by the proposed process because themeasured values are immediately taken proximal to the loading scoop. Themovement of the center of gravity from a position when the scoop isunloaded to a position after full loading by the bulk goods, is takeninto consideration so that it is also possible to obtain exact measuredvalues of the loads even while the apparatus is working on inclinedsurfaces. With the proposed method, an accurate determination of theweight of the contents of the scoop of hydraulic excavators is nowpossible.

An operational step for calculating by computer the loaded weight andthe loaded weight per unit time is illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the support arm and loading scoop of ahydraulic earth mover or excavator; and

FIG. 2 is an illustration of the force diagram useful in computing theweight of the material contained in the scoop of the excavator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As best seen in FIG. 1, the loading scoop of an earth excavator isgenerally identified as 1. Scoop 1 is rotatably pivoted about pivot 3 oflifting arm 2. A hydraulic piston-cylinder unit 4 attached on one end tolifting arm 2 at 5 serves to support and rotate the loading scoop 1.Hydraulic unit 4 is connected on its other end to point 6 of thescoop 1. Thus, scoop 1 pivots about pivot 3 by the extending andcontracting action of the hydraulic unit 4. This is the mechanism usedfor loading and unloading bulk goods into the scoop of the earthexcavator. The loading scoop 1 is shown as being filled with bulk goods7. It is an underlying assumption of the present invention that the bulkgoods contained in the scoop are uniformly distributed in the scoop 1.

The center of gravity 8 of the empty loading shovel 1 depends upon theactual weight and structure of the scoop 1 and can, in each instance, bepredetermined by computation. As best seen in FIGS. 1 and 2, the forceF₁ corresponds to the structural weight of the empty loading scoop 1 andis located and downwardly directed at the center of gravity 8. F₁ isalways located at a distance R₁ from pivot point 3. The moment of weightF₁ about pivot point 3 is F₁ ×S₁ ; but since S₁ is equal to R₁ ×Cos β(see FIG. 2) the moment of empty shovel 1 with a weight F₁ about point 3in F₁ ×R₁ ×cos β.

The force F₂, the weight sought to be determined by the presentinvention, i.e., the weight of the load in the scoop, acts at center ofgravity of the load in the shovel, i.e., at point 9. Force F₂ is alsodownwardly directed but this time acts at the center of gravity 9. Themoment of the load of material in the scoop, F₂, about pivot point 3 isF₂ ×S₂. Since the load F₂ will always have a center of gravity 9 at adistance R₂ from pivot point 3, then the moment of F₂ about pivot point3 is F₂ ×R₂ ×cos β+ρ. This, of course, assumes that the load of materialis basically uniformly loaded in scoop 1.

The moment arm S₁ of the structural weight F₁ of the scoop 1 is locatedbetween the vector force F₁ acting at center of gravity 8 and the pivotpoint 3 of the scoop 1. S₂ indicates the moment arm of force F₂ takenbetween the force F₂ acting at center of gravity 9 and the pivot point 3of the scoop 1. The distance between the centers of gravity 8, 9 of theforces F₁ and F₂, i.e., the scoop in the unloaded and fully loadedconditions, from the pivot point 3 of the scoop 1 are indicated as R₁and R₂, respectively (see FIG. 1). S₃ denotes the moment arm betweenpivot point 3 and the effective line of the force of the piston-cylinderunit 4. S₃ is measured between pivot point 3 and an imaginary linepassing through the longitudinal central axis of the piston rod 4.

Accordingly, the weight of the contents of the scoop may be determinedas follows. The hydraulic back pressure of the piston-cylinder unit 4 ismeasured between the arm 2 and the scoop 1. This can be done by apressure recorder or other pressure sensitive device. Once that pressureis determined, the following relation results from the structural weightF₁ of the unloaded scoop 1 having a moment arm distance S₁ from betweenthe center of gravity 8 to the pivot point 3 of the scoop 1, a seconddistance S₂ between the center of gravity 9 of loaded scoop 1 to pivotpoint 3 and the force F₂ of the load in the scoop acting at point 9. Themoment arm distance S₃, also acting on pivot 3, is predetermined for thepiston-cylinder unit 4.

Thus,

Pcyl×A×S₃ =F₁ ×S₁ +F₂ ×S₂ and since S₁ =R₁ ×cos β and S₂ =R₂ ×cos (β+ρ);therefore

F₂ =1/(R₂ ×cos (β+ρ)(Pcyl×A×S₃ -F₁ ×R₁ ×cos β)

wherein:

Pcyl is the pressure in the lifting cylinder;

A is the piston surface area;

Beta (β) is the measured angle between the horizontal and a lineconnecting pivot point 3 and the center of gravity 8 of the empty scoop1;

Phi (ρ) is an assumed constant angle, as shown in FIG. 2; and R₁ isknown and R₂ is assumed as known and since, as mentioned, the scoop isassumed as being uniformly loaded, R₁ and R₂ signify the distancebetween the respective centers of gravity 8 and 9 and the pivot point 3.

Apart from the measured values, i.e., the pressure in thepiston-cylinder unit 4 and the angle β, are the predetermined parametersexpressed in the formula which are dependent on the apparatus'sstructure and may be determined by computation and fed into the computerin a first operational step. Then, merely the measured values, i.e., theback pressure in the piston-cylinder unit 4 and the bailing angle β needbe fed into a computer as appropriate signals to determine the desiredloaded weight of the bulk goods F₂. In an alternate embodiment of theinvention, the loaded weights, F₂, can be accumulated and then displayedat desired intervals. The measurement step may occur in any desiredposition of the loading scoop 1 and with arm 2 in any position. It wouldbe advantageous if the measured values are determined by activating thecontrol valve for opening the lid scoop. The time delay in operating thehydraulics of the lid scoop should be adequate for a definitedetermination of the measured values. If, as proposed in the invention,the movement of the loading scoop 1 is briefly stopped, the measurementscan be quickly taken without being distorted by the movement of theloading scoop 1.

The teachings of the attached copy of the corresponding Germanapplication, upon which this application claims priority, is hereinspecifically incorporated by reference.

It should be understood, of course, that the specific form of theinvention herein illustrated and described is intended to berepresentative only, as certain changes may be made therein withoutdeparting from the clear teachings of the disclosure. Accordingly,reference should be made to the following appended claims in determiningthe full scope of the invention.

We claim:
 1. A method of measuring the loaded material of a materialloading machine having a hydraulically operable loading arm and amaterial loading scoop pivotable on said loading arm about a pivotpoint, wherein said holding scoop and said loading arm are connected bya hydraulic piston-cylinder unit located therebetween and apparatus formeasuring the bailing angle defined by the horizontal and a line passingthrough the pivot point of the scoop and the center of gravity of theempty scoop and for measuring the pressure on said hydraulicpiston-cylinder unit comprising the steps of:(a) feeding a computer thefollowing predetermined fixed values;(i) the weight of the empty scoop;(ii) the distance from the center gravity of the empty scoop to saidpivot point; (iii) the surface area of the piston of the piston-cylinderunit and the moment distance of said piston-cylinder unit to said pivotpoint; (iv) the distance from the center of gravity of the load in thescoop to said pivot point; (v) the angle between the lines connectingthe pivot point to the centers of gravity of the empty scoop and theload in the scoop; (b) loading material into the scoop; (c) measuringthe pressure in said piston-cylinder unit at least in one position ofsaid loading arm; (d) measuring said bailing angle at the same positionof said loading arm; (e) providing said measured pressure and bailingangle values to said computer; (f) computing the weight of the loadedmaterial by using said computer which bases its calculations on saidfixed predetermined values and said measured pressure and bailing anglevalues; and (g) providing an indication of the weight of said loadedmaterial.
 2. A method as claimed in claim 1, wherein:(a) said steps (c)and (d) are performed while said loading arm and scoop are momentarilyinterrupted in their motion.
 3. A method as claimed in claim 1,wherein:(a) at least two loads of said material loading machine aremeasured according to steps (a)-(f) of claim 1; and (b) said individualweights of said loads are accumulated and then indicated.
 4. A method asclaimed in claim 3, wherein:(a) said accumulated weights of said loadsare indicated at predetermined time intervals.